Text 17

tad-buddhayas tad-atmanas
tan-nisthas tat-parayanah
gacchanty apunar-avrttim
jnana-nirdhuta-kalmasah

Translation

When one’s intelligence, mind, faith and refuge are all fixed in the Supreme, then one becomes fully cleansed of misgivings through complete knowledge and thus proceeds straight on the path of liberation.

Commentary by Srila Prabhupada

The Supreme Transcendental Truth is Lord Krishna. The whole Bhagavad-gita centers around the declaration that Krishna is the Supreme Personality of Godhead. That is the version of all Vedic literature. Para-tattva means the Supreme Reality, who is understood by the knowers of the Supreme as Brahman, Paramatma and Bhagavan. Bhagavan, or the Supreme Personality of Godhead, is the last word in the Absolute. There is nothing more than that. The Lord says, mattah parataram nanyat kincid asti dhananjaya. Impersonal Brahman is also supported by Krishna: brahmano hi pratishthaham. Therefore in all ways Krishna is the Supreme Reality. One whose mind, intelligence, faith and refuge are always in Krishna, or, in other words, one who is fully in Krishna consciousness, is undoubtedly washed clean of all misgivings and is in perfect knowledge in everything concerning transcendence. A Krishna conscious person can thoroughly understand that there is duality (simultaneous identity and individuality) in Krishna, and, equipped with such transcendental knowledge, one can make steady progress on the path of liberation.

Commentary by Sri Visvanatha Cakravarti Thakur

But this vidya reveals knowledge about the jivatma, not knowledge of the paramatma.

The Lord says, bhaktyaham ekaya grahyah: I am attainable only by bhakti. Therefore the jnanais must additionally practice bhakti in order to obtain knowledge of paramatma. That is stated in this verse.

The word tat refers to the Supreme Lord previously mentioned as vibhu in verse 15. Those who place their intelligence in the Supreme Lord, who are dedicated to contemplation on the Lord using intellect (tad buddhayah), who are meditating on the Lord using the mind (tad atmanah), who fix their knowledge in the Lord, giving up sattvika knowledge of the soul apart from the body, and becoming fixed only in the Lord, (the Lord says one should place knowledge in him (jnanam ca mayi sannyaset), becoming absorbed in the processes of hearing and chanting about the Lord (tat paranayanah) do not attain birth again. As will be said later,

bhaktya mam abhijanati yavan yas casmi tattvatah
tato mam tattvato jnatva visate tad-anantaram

I am to be known in truth only by bhakti. Knowing me in truth, one attains me. BG 18.55

Those persons' ignorance has been previously completely destroyed by vidya (jnana nirdhuta kalmasah).